This invention relates to an imaging device adapting an optical printing system such as an optical printer and a photo-copy machine, and more particularly to an imaging device for developing an image on a transfer sheet by applying a pressure thereon under such condition as being superposed with a photo and pressure sensitive recording sheet on which a latent image is formed by exposing an optical image thereon.
Recently, such photo and pressure sensitive recording sheet has been proposed as being coated with photo-hardenable microcapsules containing chromogenic materials, and a visible image is developed on a separate transfer sheet coated with developing agents which react with the chromogenic materials for development. With such transfer type recording sheet, a latent image is first formed on the recording sheet by directly exposing it to a corresponding optical image and then the visible image is developed on the transfer sheet, with the result of a fine printing quality with the image of higher resolution and greater clearness than with the so far prevailing way of printing through transfer of a toner image onto a common paper.
Such transfer type recording sheet therefore tends to be used as printing paper for an optical printer and/or a photo-copy machine. For use with an optical printer, for instance, optical signals responsive to characters and/or picture informations output from a computer are first projected to the recording sheet to form a latent image thereon.
As the photo-hardenable microcapsules, microcapsules enveloping photo-hardenable resins therein has been used because it is versatile and easily available. With such microcapsules, when the pressure is applied thereto, the microcapsules which are not hardened yet as being not exposed to light are ruptured to allow chromogenic materials therein to stream out and react with the developing agents on the transfer sheet for development.
However, these has arised a problem here that is, when the recording sheet is set to be as wide as the transfer sheet, the edge of the transfer sheet may not be developed if the sheets are widthwise offset from each other. It takes a higher cost to design the device such that the both sheets should exactly overlap each other with no edge sticking one out of the other. Fruthermore, in a design where the recording sheet is pinched at its both edges by pinch rollers which are rotated to feed the sheet in a certain direction before exposure, the microcapsules at these edges of the recording sheet may be ruptured by the pinch rollers so that it becomes impossible to use such edge portions of the recording sheet for forming a latent image thereon. Thus, the width of the recording sheet is set to be wider than that of the transfer sheet for the reasons mentioned above.
With the recording sheet wider than the transfer sheet as described above, when the recording sheet overlying the transfer sheet are inserted together between the pressing rollers, the unhardened microcapsules on the edge portions of the recording sheet sticking out of the transfer sheet are ruptured to cause the chromogenic materials and photo-hardenable resins to stream out and stick to the roller surfaces. The deposit is thickened on the roller surfaces with extended use of the optical printing device and finally causes a change in pressure applied by the pressing rollers, which results in incomplete rupturing of the unhardened microcapsules and therefore irregular development of the image on the transfer sheet. Also, the deposit on the pressing rollers sometimes soil the subsequent transfer sheet so that extra maintenance becomes required, for instance, for cleaning the pressing rollers more frequently.